What ammunition does a Marlin 1887 shoot if it has 32W stamped under the hex barrel?

I'm assuming you have a Marlin model 1889, not 1887, as they never made a model 1887. The 1889 does have a patent date of 1887 on the barrel, so this is a common mistake. Any Marlin marked ".32W" on the barrel will normally be chambered for the .32-20 Win. cartridge.